Heat oven to 250°F. Spray 13 x 9-inch baking pan with cooking spray. Combine cereal and pretzels in pan; mix well. Place oil in a small bowl. Stir in mustard, honey, garlic salt and onion salt; mix well. Pour over cereal mixture; stir to coat evenly. Bake 1 hour, stirring every 15 minutes. Transfer to baking sheet, spreading mixture in even layer. Cool completely. Makes about 20 servings (1/2 cup servings). Store tightly covered at room temperature up to 5 days.